CSYNOPSIS

DESCRIPTION

Some functionality specific to the XFS filesystem is accessible to
applications through platform-specific system call interfaces. These
operations can be divided into two sections - operations that operate
on individual files, and operations that operate on the filesystem
itself. Care should be taken when issuing xfsctl() calls to ensure the
target path and file descriptor (both must be supplied) do indeed
represent a file from an XFS filesystem. The statfs(2) and fstatfs(2)
system calls can be used to determine whether or not an arbitrary path
or file descriptor belong to an XFS filesystem. These are not portable
however, so the routines platform_test_xfs_fd() and
platform_test_xfs_path() provide a platform-independent mechanism.
FileOperations
In order to effect an operation on an individual file, the pathname and
descriptor arguments passed to xfsctl identifies the file being
operated on. The final argument described below refers to the final
argument of xfsctl. All of the data structures and macros mentioned
below are defined in the <xfs/xfs_fs.h> header file.
XFS_IOC_ALLOCSPXFS_IOC_ALLOCSP64XFS_IOC_FREESPXFS_IOC_FREESP64
Alter storage space associated with a section of the ordinary
file specified. The section is specified by a variable of type
xfs_flock64_t, pointed to by the final argument. The data type
xfs_flock64_t contains the following members: l_whence is 0, 1,
or 2 to indicate that the relative offset l_start will be
measured from the start of the file, the current position, or
the end of the file, respectively (i.e., l_start is the offset
from the position specified in l_whence). If the offset
specified is before the current end of file, any data previously
written into this section is no longer accessible. If the
offset specified is beyond the current end of file, the file is
grown and filled with zeroes. The l_len field is currently
ignored, and should be set to zero.
XFS_IOC_ALLOCSP, XFS_IOC_ALLOCSP64, XFS_IOC_FREESP and
XFS_IOC_FREESP64 operations are all identical.
XFS_IOC_FSSETDM
Set the di_dmevmask and di_dmstate fields in an XFS on-disk
inode. The only legitimate values for these fields are those
previously returned in the bs_dmevmask and bs_dmstate fields of
the bulkstat structure. The data referred to by the final
argument is a structfsdmidata. This structure’s members are
fsd_dmevmask and fsd_dmstate. The di_dmevmask field is set to
the value in fsd_dmevmask. The di_dmstate field is set to the
value in fsd_dmstate. This command is restricted to root or to
processes with device management capabilities. Its sole purpose
is to allow backup and restore programs to restore the
aforementioned critical on-disk inode fields.
XFS_IOC_DIOINFO
Get information required to perform direct I/O on the specified
file descriptor. Direct I/O is performed directly to and from a
user’s data buffer. Since the kernel’s buffer cache is no
longer between the two, the user’s data buffer must conform to
the same type of constraints as required for accessing a raw
disk partition. The final argument points to a variable of type
structdioattr, which contains the following members: d_mem is
the memory alignment requirement of the user’s data buffer.
d_miniosz specifies block size, minimum I/O request size, and
I/O alignment. The size of all I/O requests must be a multiple
of this amount and the value of the seek pointer at the time of
the I/O request must also be an integer multiple of this amount.
d_maxiosz is the maximum I/O request size which can be performed
on the file descriptor. If an I/O request does not meet these
constraints, the read(2) or write(2) will fail with EINVAL. All
I/O requests are kept consistent with any data brought into the
cache with an access through a non-direct I/O file descriptor.
XFS_IOC_FSGETXATTR
Get additional attributes associated with files in XFS file
systems. The final argument points to a variable of type structfsxattr, whose fields include: fsx_xflags (extended flag bits),
fsx_extsize (nominal extent size in file system blocks),
fsx_nextents (number of data extents in the file). A
fsx_extsize value returned indicates that a preferred extent
size was previously set on the file, a fsx_extsize of zero
indicates that the defaults for that filesystem will be used.
Currently the meaningful bits for the fsx_xflags field are:
Bit 0 (0x1) - XFS_XFLAG_REALTIME
The file is a realtime file.
Bit 1 (0x2) - XFS_XFLAG_PREALLOC
The file has preallocated space.
Bit 3 (0x8) - XFS_XFLAG_IMMUTABLE
The file is immutable - it cannot be modified, deleted
or renamed, no link can be created to this file and no
data can be written to the file. Only the superuser
or a process possessing the CAP_LINUX_IMMUTABLE
capability can set or clear this flag.
Bit 4 (0x10) - XFS_XFLAG_APPEND
The file is append-only - it can only be open in
append mode for writing. Only the superuser or a
process possessing the CAP_LINUX_IMMUTABLE capability
can set or clear this flag.
Bit 5 (0x20) - XFS_XFLAG_SYNC
All writes to the file are synchronous.
Bit 6 (0x40) - XFS_XFLAG_NOATIME
When the file is accessed, its atime record is not
modified.
Bit 7 (0x80) - XFS_XFLAG_NODUMP
The file should be skipped by backup utilities.
Bit 8 (0x100) - XFS_XFLAG_RTINHERIT
Realtime inheritance bit - new files created in the
directory will be automatically realtime, and new
directories created in the directory will inherit the
inheritance bit.
Bit 9 (0x200) - XFS_XFLAG_PROJINHERIT
Project inheritance bit - new files and directories
created in the directory will inherit the parents
project ID. New directories also inherit the project
inheritance bit.
Bit 10 (0x400) - XFS_XFLAG_NOSYMLINKS
Can only be set on a directory and disallows creation
of symbolic links in that directory.
Bit 11 (0x800) - XFS_XFLAG_EXTSIZE
Extent size bit - if a basic extent size value is set
on the file then the allocator will allocate in
multiples of the set size for this file (see
XFS_IOC_FSSETXATTR below).
Bit 12 (0x1000) - XFS_XFLAG_EXTSZINHERIT
Extent size inheritance bit - new files and
directories created in the directory will inherit the
parents basic extent size value (see
XFS_IOC_FSSETXATTR below). Can only be set on a
directory.
Bit 13 (0x2000) - XFS_XFLAG_NODEFRAG
No defragment file bit - the file should be skipped
during a defragmentation operation. When applied to a
directory, new files and directories created will
inherit the no-defrag bit.
Bit 14 (0x4000) - XFS_XFLAG_FILESTREAM
Filestream allocator bit - allows a directory to
reserve an allocation group for exclusive use by files
created within that directory. Files being written in
other directories will not use the same allocation
group and so files within different directories will
not interleave extents on disk. The reservation is
only active while files are being created and written
into the directory.
Bit 31 (0x80000000) - XFS_XFLAG_HASATTR
The file has extended attributes associated with it.
XFS_IOC_FSGETXATTRA
Identical to XFS_IOC_FSGETXATTR except that the fsx_nextents
field contains the number of attribute extents in the file.
XFS_IOC_FSSETXATTR
Set additional attributes associated with files in XFS file
systems. The final argument points to a variable of type structfsxattr, but only the following fields are used in this call:
fsx_xflags and fsx_extsize. The fsx_xflags realtime file bit
and the file’s extent size may be changed only when the file is
empty, except in the case of a directory where the extent size
can be set at any time (this value is only used for regular file
allocations, so should only be set on a directory in conjunction
with the XFS_XFLAG_EXTSZINHERIT flag).
XFS_IOC_GETBMAP
Get the block map for a segment of a file in an XFS file system.
The final argument points to an arry of variables of type structgetbmap. All sizes and offsets in the structure are in units of
512 bytes. The structure fields include: bmv_offset (file
offset of segment), bmv_block (starting block of segment),
bmv_length (length of segment), bmv_count (number of array
entries, including the first), and bmv_entries (number of
entries filled in). The first structure in the array is a
header, and the remaining structures in the array contain block
map information on return. The header controls iterative calls
to the XFS_IOC_GETBMAP command. The caller fills in the
bmv_offset and bmv_length fields of the header to indicate the
area of interest in the file, and fills in the bmv_count field
to indicate the length of the array. If the bmv_length value is
set to -1 then the length of the interesting area is the rest of
the file. On return from a call, the header is updated so that
the command can be reused to obtain more information, without
re-initializing the structures. Also on return, the bmv_entries
field of the header is set to the number of array entries
actually filled in. The non-header structures will be filled in
with bmv_offset, bmv_block, and bmv_length. If a region of the
file has no blocks (is a hole in the file) then the bmv_block
field is set to -1.
XFS_IOC_GETBMAPA
Identical to XFS_IOC_GETBMAP except that information about the
attribute fork of the file is returned.
XFS_IOC_RESVSPXFS_IOC_RESVSP64
This command is used to allocate space to a file. A range of
bytes is specified using a pointer to a variable of type
xfs_flock64_t in the final argument. The blocks are allocated,
but not zeroed, and the file size does not change. If the XFS
filesystem is configured to flag unwritten file extents,
performance will be negatively affected when writing to
preallocated space, since extra filesystem transactions are
required to convert extent flags on the range of the file
written. If xfs_info(8) reports unwritten=1, then the
filesystem was made to flag unwritten extents.
XFS_IOC_UNRESVSPXFS_IOC_UNRESVSP64
This command is used to free space from a file. A range of
bytes is specified using a pointer to a variable of type
xfs_flock64_t in the final argument. Partial filesystem blocks
are zeroed, and whole filesystem blocks are removed from the
file. The file size does not change.
XFS_IOC_PATH_TO_HANDLEXFS_IOC_PATH_TO_FSHANDLEXFS_IOC_FD_TO_HANDLEXFS_IOC_OPEN_BY_HANDLEXFS_IOC_READLINK_BY_HANDLEXFS_IOC_ATTR_LIST_BY_HANDLEXFS_IOC_ATTR_MULTI_BY_HANDLEXFS_IOC_FSSETDM_BY_HANDLE
These are all interfaces that are used to implement various
libhandle functions (see open_by_handle(3)). They are all
subject to change and should not be called directly by
applications.
FilesystemOperations
In order to effect one of the following operations, the pathname and
descriptor arguments passed to xfsctl() can be any open file in the XFS
filesystem in question.
XFS_IOC_FSINUMBERS
This interface is used to extract a list of valid inode numbers
from an XFS filesystem. It is intended to be called
iteratively, to obtain the entire set of inodes. The
information is passed in and out via a structure of type
xfs_fsop_bulkreq_t pointed to by the final argument. lastip is
a pointer to a variable containing the last inode number
returned, initially it should be zero. icount is the size of
the array of structures specified by ubuffer. ubuffer is the
address of an array of structures, of type xfs_inogrp_t. This
structure has the following elements: xi_startino (starting
inode number), xi_alloccount (count of bits set in
xi_allocmask), and xi_allocmask (mask of allocated inodes in
this group). The bitmask is 64 bits long, and the least
significant bit corresponds to inode xi_startino. Each bit is
set if the corresponding inode is in use. ocount is a pointer
to a count of returned values, filled in by the call. An output
ocount value of zero means that the inode table has been
exhausted.
XFS_IOC_FSBULKSTAT
This interface is used to extract inode information (stat
information) "in bulk" from a filesystem. It is intended to be
called iteratively, to obtain information about the entire set
of inodes in a filesystem. The information is passed in and out
via a structure of type xfs_fsop_bulkreq_t pointed to by the
final argument. lastip is a pointer to a variable containing
the last inode number returned, initially it should be zero.
icount indicates the size of the array of structures specified
by ubuffer.ubuffer is the address of an array of structures of
type xfs_bstat_t. Many of the elements in the structure are the
same as for the stat structure. The structure has the following
elements: bs_ino (inode number), bs_mode (type and mode),
bs_nlink (number of links), bs_uid (user id), bs_gid (group id),
bs_rdev (device value), bs_blksize (block size of the
filesystem), bs_size (file size in bytes), bs_atime (access
time), bs_mtime (modify time), bs_ctime (inode change time),
bs_blocks (number of blocks used by the file), bs_xflags
(extended flags), bs_extsize (extent size), bs_extents (number
of extents), bs_gen (generation count), bs_projid (project id),
bs_dmevmask (DMIG event mask), bs_dmstate (DMIG state
information), and bs_aextents (attribute extent count). ocount
is a pointer to a count of returned values, filled in by the
call. An output ocount value of zero means that the inode table
has been exhausted.
XFS_IOC_FSBULKSTAT_SINGLE
This interface is a variant of the XFS_IOC_FSBULKSTAT interface,
used to obtain information about a single inode. for an open
file in the filesystem of interest. The same structure is used
to pass information in and out of the kernel, except no output
count parameter is used (should be initialized to zero). An
error is returned if the inode number is invalid.
XFS_IOC_THAWXFS_IOC_FREEZEXFS_IOC_GET_RESBLKSXFS_IOC_SET_RESBLKSXFS_IOC_FSGROWFSDATAXFS_IOC_FSGROWFSLOGXFS_IOC_FSGROWFSRTXFS_IOC_FSCOUNTS
These interfaces are used to implement various filesystem
internal operations on XFS filesystems. For XFS_IOC_FSGEOMETRY
(get filesystem mkfs time information), the output structure is
of type xfs_fsop_geom_t. For XFS_FS_COUNTS (get filesystem
dynamic global information), the output structure is of type
xfs_fsop_counts_t. The remainder of these operations will not
be described further as they are not of general use to
applications.